1. Field of the Invention
The present invention relates generally to shutter release mechanisms for cameras, and more particularly to shutter release mechanisms which can prevent undesired shutter actuation.
2. Description of the Prior Art
Those versed in the prior art dealing with shutter release mechanisms in still-picture cameras are aware of at least several alternate design approaches for preventing undesired shutter actuation using such release mechanisms. According to one design, a locking device is provided in a camera to block manual depression of a shutter release member by the camera user. The locking device blocks the shutter release member usually to prevent unintended double exposure or because there is too much or too little light to obtain a proper exposure. While such shutter release locking devices have been available for many years, the difficulty with many of their commercial embodiments is that they can cause camera damage through undue pressure being applied to the shutter release member by the camera user.
Another known design for preventing undesired shutter actuation calls for the camera to display a visual signal in its viewfinder during the initial stage of manually depressing the shutter release member. The signal is displayed when the level of available light is unsuitable for a proper exposure. The disadvantage of this design is that the visible signal is not a positive means for preventing shutter actuation. That is, the camera user may fail to observe the visible signal or forget about its appearance in the viewfinder when depressing the shutter release member.
A third design which has been recently devised is intended for use in automatic exposure cameras. According to this approach, which is disclosed in U.S. Pat. No. 3,690,228, granted Sept. 12, 1972, the shutter release member is normally connected by way of an interlocking member to a latch member which operates to restrain a shutter drive member. During the initial stage of manually depressing the shutter release member, the position of an exposure meter pointer is detected by mechanical means. If the pointer is located outside an automatic exposure range, the interlocking member is disconnected from the shutter release member and the latch member. As a result, the release member cannot actuate the camera shutter even though still able to be depressed. While this more recent design may be considered in some ways to represent an improvement over the other prior art examples discussed, it suffers from the possibility of mechanical failure because of the detailed mechanical relation between the exposure meter pointer and the means for disconnecting the interlocking member from the shutter release and latch members.